Defrosting control



Patented Feb. 13, 1951 DEFROSTING CONTROL James B. Bader, Webster Groves, Mo., assigner, by mesne assignments, to Missouri Automatic Control Corporation, a corporation of Missouri Application December 3, 1945, Serial No. 632,469

17 Claims. (Cl. (i2-4) The present invention relates generally to refrigeration equipment and, more particularly, to control systems therefor.

The problem of maintaining the refrlgerating coils of a mechanical refrigeratlng system. or the like, free from accumulations of ice is one of long standing. The incrustations which form on the coils of such systems reduce the efficiency of the refrigeration and, hence, must be removed periodically. In the earlier household refrigerators and larger installations, such as walk-in coolers and the like, defrosting of the coils is accomplished through manual controls. In more recent refrigeration systems, defrosting controls include semi-automatic features. Automatic control for the defrosting of refrigeration systems, manifestly, is the long sought goal.

Therefore, an object of the present invention ls to provide a novel control system for a refrigeration system which is fully automatic in defrosting of the refrigeration coils.

Another object is to provide a novel control system for mechanical refrigeration systems having defrosting heaters which automatically energizes the heaters as required.

Another object is to provide a novel control system for refrigeration systems having defrosting heaters, in which a particular heater is set or cocked for energization only after the enclosure temperature has acquired a minimum value as defined by the setting of an enclosure thermostat.

Another object is to provide a novel refrigeration system in which the defrosting of the cooling unit is fully automatic.

Another object is to provide a novel refrigeration system in which defrosting of the cooling unit is periodically eiected through the automatic energization of a heater unit disposed adjacent the cooling unit.

The foregoing and other objects and advantages are apparent from the following description taken with the accompanying drawing, in which:

Fig. 1 is a schematic diagram of one embodiment of the present invention as applied to a mechanical refrigeration system, the several units being shown diagrammatically; and

Fig. 2 is a front view of the control box of a control unit, as contemplated by the present invention.

Referring to the drawing more particularly by reference numerals, Fig. 1 shows schematically a refrigeration system embodying the teachings of the present invention. Broadly, the refrigeration system includes an enclosure differential thermostat I 0. two interconnected control differential thermostats I2 and I4, a cooling unit I6 including a fan I8 and a cooling coil 20, a defrosting heater 22, a compressor 24, and suitable electrical wiring. The refrigerant lines between the cooling coil 20 and the compressor 24 are shown as broken to indicate that the usual elements of a refrigeration system including a condenser are incorporated by inference.

The cooling unit I6 and heater 22 are mounted suitably in a household refrigerator box, a walkin cooler, or the like, the thermostats I0, I2 and I4 normally being mounted externally thereof for control convenience, although they may be in the cooled area if desired. The compressor is disposed outside the cooled enclosure.

The differential thermostats I0, I 2! and I4 preferably are of the same type. Since the thermostats I0, I2 and I4 are identical with the exception of a feature in thermostat II) mentioned below, only one device is described specifically as to the details shown.

The differential thermostat I2 takes the general form of the thermostat shown in U. S. Patent No. 2,291,502, to L. M. Persons, granted July 28, 1942. A casing 26 contains the elements of the thermostat I2, which include a movable conducting arm 28 carrying opposed contacts 30 and 32 adjacent one end and fulcrumed adjacent the other end between two adjustable pivot points 34 and 36, providing for the differential setting and adjustment of the thermostat. The contacts 3U and 32 make and break with stationary contacts 3l and 33, respectively. A second arm 38, pivoted at to the casing 26, is connected by a leaf spring 42 to the movable arm 28. The arm 38 `is biased by a spring 44 into engagement with a sleeve 46, which is adjustably threaded onto a stud 48. An adjusting knob is mounted on the other end of the sleeve 46, exteriorly of a cover plate 52. A diaphragm cup 54 is: secured to the back of the casing 26 and carries therein a movable diaphragm 56.wl1ich, with the bottom of the cup 54, forms a chamber 58. Communicating with the chamber 56 is a capillary tube BIJ which is connected at its other end to a bulb 62, the chamber 58, the tube 50, and the bulb 62 being lled with a suitable expansible uid.

The operation and function of differential thermostats, such as the thermostat I2, are well known in the art and require no detailed explanation, the disclosure of the abovementioned Persons patent in respect thereto being incorporated herein by reference.

The thermostat I4 is identical with the thermostat I2. The thermostat I8 is dill'erent in construction from the thermostat I2 only in one feature; namely, the arm 28h is of composite construction, including a base portion 84 of insulating material to which is connected a conducting portion 68, which carries only a single contact 88 adapted to make and break with a contact 18.

The fan |8, the coil 28, and the heater 22 are mountedin a cabinet l2 having opposite walls 'I4 and I8 which are equipped with gravity closing louvers 18. When the fan I8 is in operation, the louvers' 18 will assume some such position such as that shrown in the drawing.

The bulb 82h of the thermostat I8 is disposed within the cooled enclosure at a point suitable for proper control of the temperature. 'I'he bulbs 82 and 82a of the thermostats I2 and I4, respectively, are disposed within the cabinet 'I2 and are aiected by the temperature within the cabinet 'l2 in the manner set forth below.

Electrical power for operation of the several units is supplied by power lines 88 and 82. Line I8 is connected to the conducting portion 88 of the thermostat I8. A conducting wire 84 connects the stationary contact 'I8 of the thermostat I8 and the movable arm 28 of the thermo- 'stat I2. A conducting wire 88 connects the stationary contact 3| of the thermostat I2 to one terminal of the fan I8, the other terminal of the fan I8 being connected by a conducting wire 88 to the power line 82. A conducting wire 88 connects the stationary contact 33 of the thermostat i2 to the movable arm 28a of the thermostat I4.

The stationary contact 3|a of the thermostat I4 is connected by a conducting wire 82 to one terminal of the defrosting heater 22, the other terminal of the defrosting heater 22 being connected by a conducting wire 84 to the power line 82. The stationary contact 33a of the thermostat I4 is connected by a conducting wire 8l to the conducting wire 88 which, in turn, leads to thefan I8 and then to the power line 82. The compressor 24 is connected through one terminalby a conducting wire 88 with the conducting wire 88, and through the other terminal by a conducting wire |88 to the power line 82.

In Fig. 2, the interconnected thermostats I2 and I4 are shown mounted on a control box |82. being secured thereto by screws |84. A conduit |88 receives the several conducting wires which lead to the thermostat I8. the fan I8, the heater 22, and the compressor 24.

Operation For purposes of illustration of operation, it will be assumed that the differential thermostat Il is set to close the contacts 88 and I8 at 15", and to open the same at -20; that the diilerential thermostat I2 is set to close the contact 32 with the contact 33 at -10 and to open these contacts and to close the contact 38 with the contact 3| at -15; and that the differential thermostat I4 is set to close the contact 32a with the contact 33a at +33 and to open these contacts and to close the contact 38a with the contact 3 Ia. at -20.

It will be further assumed that the enclosure, cooled by the present refrigeration system, is warm and requires cooling. Hence, the expansion of the uid in the bulb 82D of the thermostat I8 under such warm temperature will have closed the contact 88 with the contact 18. thereby supplying current from the power line 88 which passes through the conducting wire 84 to the conducting arm 28 of the thermostat I2. Ines-- bulb 82 will have expanded to close the movable contact 32 with the stationary contact 33. Hence, the current will flow from the arm 28 through the contacts 32 and 33, and through the conducting wire 98 to the movable conducting arm 28a. The fluid in the bulb 82a being warm will have closed the movable contact 32a with the stationary contact 33a. Therefore, current will flow from the arm 28a through the contacts 32a and 33a, and, consecutively, through the conducting wire 86, the conducting wire 88, the two terminals of the fan I8, the conducting wire 8l, and the power line 82, thereby energizing the fan I8. Simultaneously, the current llows consecutively through the conducting wire 88, the conducting wire 88, the conducting wire 88, the terminals of the compressor 24, the conducting wire |88, and the power line 82, thereby energizing the compressor, which is in parallel with the fan I8. Energization of the compressor 24 eiects cooling of the coil 28 to which the compressor is connected, as shown, air from the cooled enclosure being blown across the coil 28, through the right hand louvers 18. and to the cooled enclosure by the fan I8.

As the compressor 24 continues to function, the temperature in the cooled enclosure and in the cabinet l2 will continue to drop. When the temperature drops to -l5, the movable arm 28 will be actuated by the iluid in the tube 82 to break contacts 32 and 33 and to engage contact 38 with contact 3|. This is true since the thermostat I2 is assumed to cycle between -'10 and -15. The closing of contact 38 with 3| and the breaking of contact 32 with 33 eiects no immediate change in the operation of the system since the fan I8 and the compressor 24 are still energized, the conducting wire 86 supplying the current path instead of the conducting wires 88 and 98 and the conducting elements of the thermostat I4.

As the temperature of the cooled enclosure and in the cabinet 'l2 drops to -20, which is the lower temperature of the cooled enclosure cycle, the uid vin the tube 62a will have contracted to snap the contact 38a into engagement with the contact 3 Ia, breaking the engagement of the contact 32a with the contact 33a. This action cocks, or sets, the circuit of the defrosting heater 22, no

current passing through the heater 22 as yet since the circuit therethrough is complete only when the contacts 32 and 33 of the thermostat I2 are in engagement, the contacts 32 and 33, at this point in the refrigeration cycle, being out of engagement, as aforesaid.

Also, as the temperature drops to 20, the fluid in the tube 62h of the thermostat I8 will `break engagement of the contacts 88 and 18,

thereby deenergizing the whole system and stopping the fan I8 and the compressor 24. The temperature in the cooled enclosure will rise to -l5, whereupon the contact 68 will again be made by the uid in the tube B2b to engage the contact l0, starting the compressor 24 and the Ian I8.

As the compressor 24 continues to intermittently operate, frost will be formed and continue to build up on the coil 28. Since the frost forming on the coil 28 impairs the eillciency thereof, the temperature in the cooled enclosure will gradually rise. When this temperature reaches 10", the contacts 38 and 3| of the thermostat I2 will be snapped apart and the contacts 32 and 33 engaged through the action of the uid in the tube 82. The contacts 68 and 18 oi' the thermomuch as the cabinet 'I2 is warm, the tluid in the u stat I8 are closed since the temperature o! -10 is greater than the high cycle point of the thermostat I0. The breaking of the contacts 30 and 3l stops the compressor 24 and the fan I8. However, the circuit through the defrosting heater 22 is now closed, the current passing in succession throughthe conducting wire 80, the conducting portion 66 of the thermostat Il), the contacts 6l and 10, the conducting wire B4, the conducting arm 28, the contacts 32 and 33, the conducting wire 90, the conducting arm 28a, the contacts 30a and 3 la, the conducting wire 92, the terminals of defrosting heater 22, the conducting wire 94, and the power line 82. Since the fan IB is deenergized, the louvers 18 fall by gravity and close the cabinet l2. The heater 22 raises the temperature in the cabinet 12, thereby melting the frost on the coil 20. The temperature in the cabinet `l2 continues to rise until a temperature of +33 is reached, at which temperature the fluid in the tube 62a will have expanded to a point to break engagement of the contacts 30a and 3Ia of the thermostat I4 and snap the contact 32a into engagement with the contact 33a which breaks the heater circuit and again completes the circuits of the compressor 24 and the fan I8, thereby returning the system to the freezing operation.

It is clear from the foregoing that the present novel control system automatically defrosts the coil of the refrigeration system in accordance with predetermined settings of the several thermostats. Once the predetermined settings are established, it is unnecessary to give further attention to defrosting of the cooling coil. It is further manifest that the present novel refrigeration system is very flexible in respect to control settings and operation.

Modifications of the present system in its several components will be manifest to those skilled in the art. Such modifications are considered to be within the scope of the present invention, the present invention not being limited by the illustrative example but being defined by the appended claims.

What is claimed is:

1. In combination, in a refrigeration system including a cooling coil, a compressor, a coil defrosting heater, an enclosure thermostat, a first differential thermostat adjusted to operate within a range above the differential range of such enclosure thermostat, and a second differential thermostat adjusted to a differential temperature range embracing those of said enclosure and said first thermostats and to include in its upper limit the melting point of ice, such enclosure` thermostat and said rst and secondv thermostats being interconnected with each other and to said compressor and to said heater to control the operation of such compressor and heater whereby the latter element is rendered operative only after a temperature condition exists in said enclosure defined by a lower limit setting of said enclosure thermostat.

2. In combination, in a refrigeration system including a cooling coil, a compressor, defrosting heater, an enclosure thermostatic two-position switch, a first and a second control unit thermostatic two-position switch, means associated with each switch for adjusting the same to be operated with a temperature differential between a high and a low limit, a source of electrical supply connectable through said enclosure thermostatic switch and said first and second thermostatic switches to drive such compressor and to energize such heater, said control switches being interconnected with such compressor and heater whereby upon the occurrence of a temperature condition within said enclosure equal to the high limit of such enclosure switch, the same will be conditioned to close to its first position andpass electrical current through said first and second switches in the first positions thereof to drive such compressor, said flrst switch closing to its second position when the enclosure temperature drops tothe lower limit of the first switch, the second switch closing to its second position to permit energization of such heater when the enclosure temperature drops to the lower limit thereof.

3. In combination, in a refrigeration system, cooling coils, a defrosting heater therefor. a defrosting heater for cooling coils and having an enclosure differential thermostat, a first control differential thermostat, and a second control diiferential thermostat, said control thermostats being interconnected and including leads to such heater and such enclosure thermostat so interrelated that such heater will be energized automatically only after a temperature condition in the cooled enclosure of such refrigeration equipment equivalent to a minimum setting of such enclosure thermostat.

4. In combination, a first control differential thermostat, a second control differential thermostat, said thermostats being interconnected and being connected to the compressor, the defrosting heater and the enclosure thermostat of a refrigeration system including a circuit through one of said control thermostats and such heater which is set for subsequent energization upon the occurrence of a predetermined minimum temperature in an enclosure cooled by such refrigeration system, said circuit being adapted to be energized upon the occurrence in such cooled enclosure of a temperature equivalent to the higher setting of the first control thermostat.

5. In combination, a first control differential thermostat including two operative contact positions, a second control differential thermostat including two operative contact positions, said control thermostats being interconnected, said control thermostats being connected to the compressor, the defrosting heater and the enclosure differential thermostat of a refrigeration system so that automatic cyclical operation of such heater and such compressor obtains, the second control thermostat being adapted to set the circuit through such heater upon the occurrence in the cooled enclosure of the minimum temperature of such enclosure thermostat, said first control thermostat being adapted to keep closed a circuit through such compressor when said first thermostat is in a first contact position and said second control thermostat is in said heater setting contact position, said first control thermostat being adapted to interrupt the circuit through such compressor and to energize the circuit through such heater when said first control thermostat is in its second contact position and said second control thermostat is in said heater setting contact position.

6. In a refrigerating system, in combination, a compressor, a cooling coil, a defrosting heater adjacent said cooling coil, an enclosure thermostat, a first control differential thermostat, a second control differential thermostat, said control thermostats being connected to each other and to the said enclosure thermostat, to the said heater and to the said compressor in a relationship to effect cylical energization of the compressor and the heater. I

7. In a refrlgerating system, in combination, a compressor, a cooling coil, a defrosting heater adjacent said cooling coil, an enclosure thermostat, a first control differential thermostat, av second control differential thermostat, said control thermostats being connected to each other and to the said enclosure thermostat, the said heater and the said compressor to cyclically energize the compressor and the heater, said heater being connected to said control thermostats so that a heater circuit is automatically set for energization only after a temperature condition exists within the cooled enclosure equivalent to a minimum setting value for the enclosure differential thermostat.

8. In a refrigerating system, in combination, a cooled enclosure, a compressor. a cooling coil, a defrosting heater adjacent said cooling coil,

an enclosure differential thermostat, a first control differential thermostat, a second control differential thermostat, said control thermostats being electrically connected to each other and to said enclosure thermostat, to said heater, and to said compressor motor so that the occurrence in the cooled enclosure of the minimum temperature of the enclosure thermostat sets for subsequent energization a circuit through the heater and the second control thermostat, said set circuit being adapted to be energized upon the occurrence in the cooled enclosure of a temperature higher than the upper temperature setting of the enclosure thermostat and equal to the upper setting of the first control thermostat.

9.` In a refrigerating system, in combination, a cooled enclosure, a compressor, a cooling coil, a `defrosting heater adjacent said cooling coil, an enclosure differential thermostat, a rst control diferential thermostat, a second control differential thermostat, said control thermostats being electrically connected to each other and to said enclosure thermostat, to said heater, and to said compressor so that the occurrence in the cooled enclosure of the minimum temperature of the enclosure thermostat sets for subsequent energization a circuit through the heater and the Second control thermostat, said set circuit being adapted to be energized upon the occurrence in the cooled enclosure of a temperature higher than the upper temperature setting of the enclosure thermostat and equal to the upper setting of the rst control thermostat, said heater circuit being adapted to be deenergized upon the occurrence of a temperature near the coollng coil equal to the upper setting of said second thermostat, said compressor being adapted to be energized upon deenergization of said heater circuit.

10. In a refrigerating system, in combination, a cooled enclosure. a cooled enclosure differential thermostat, a cooling unit disposed in the cooled enclosure and comprising a fan and a cooling coil, a defrosting heater disposed adjacent the cooling coil, a compressor connected to the cooling coil and adapted to supply coolant therethrough, a first control differential thermostat, and a second control differential thermostat, each of said control thermostats including a first and a. second operative contact position, said control thermostats being so connected to said enclosure thermostat, said fan, said compressor, and said defrostingheater and being so interconnected with each other, that with the enclosure thermostat demanding cooling said fan and compressor are energized when the first control thermostat is in its second contact position or when said rst control thermostat is in its first contact position and said second control thermostat is in its first contactposition, said defrosting heater being energized and said fan and said compressor being deenergized when said first control thermostat is in its first contact position and said second control thermostat is in its second contact position.

11. In combination with an enclosure refrigerating device having a compressor, defrosting heater, and an enclosure thermostatic two-position switch, a first and a second control unit thermostatic two-position switch, means associated with each switch for adjusting the same to be operated with a temperature differential between a high and a low limit, a source of electrical supply connectable through said enclosure thermostatic and said first and second thermostatic switches to drive such compressor and to energize such heater, said control switches being interconnected with such compressor and heater whereby upon the occurrence of a temperature condition within said enclosure equal tothe high limit of such enclosure switch, the same will be conditioned to close to its first position and pass electrical current through said first and second switches in the first positions thereof to drive such compressor, said first switch closing to its second position when the enclosure temperature drops to the lower limit of the first switch, the second switch closing to its second position to permit energization of such heater when the enclosure temperature drops to the lower limit thereof.

l2. In combination with an enclosure refrigerating device having a compressor, defrosting heater, and an enclosure thermostatic two-position switch, a first and a second control unit thermostatic two-position switch, means associated with each switch for adjusting the same to be operated with a temperature differential between a high and a low limit. a source of electrical supply connectable through said enclosure thermostatic switch and said first and second thermostatic switches to drive such compressor and to energize such heater, said control switches being interconnected with such compressor and heater whereby upon the occurrence of a temperature condition within said enclosure equal to the high limit of such enclosure switch, the same .will be conditioned to close to its rst position and pass electrical current through said first and second switches in the first positions thereof to drive such compressor, said first switch closing to its second position when the enclosure temperature drops to the lower limit of the first switch, the second switch closing to its second position to permit energization of such heater when the enclosure temperature drops to the lower limit thereof, said second switch closing to its first position upon an enclosure temperature rise to its high limit to deenergize such heater and to reenergize the compressor, said first switch and said enclosure switch remaining in `first positions during the energization period of the heater, whereby continuous cyclical operation including cooling and defrosting obtains.

13. A method of cyclically operating a refrigeration system to automatically defrost the evaporator coil upon temperature conditions existing in the evaporator enclosure including the steps of cooking a defrosting heater circuit after an evaporator enclosure temperature equal to or greater the evaporator enclosure until the evaporator efliciency drops a predetermined amount through icing, energizing the defrosting heater circuit as enclosure temperature reaches a predetermined high due to icing of the evaporator, deenergizing the defrosting heater circuit and reenergizing the compressor as enclosure temperature reaches a further predetermined high, and repeating the steps.

14. In a control system for an enclosure refrigerating device having an electrically operated prime mover for driving the same and a coil defrosting heater, a first thermo-switch adjustable to close to a first contact at a selected high temperature and to open at a selected low temperature, a second thermo-switch having first and second contacts and a conducting member movable between and alternately into engagement with the contacts, and a third thermo-switch having rst and second contacts and a conducting member movable between and alternately into engagement with the contacts, the rst and second contacts of said second and third thermoswitches being alternately engageable by said conducting member at the limits of a temperature differential range, said thermo-switches being connected to pass current to such prime mover when the first and third switches are in their rst positions and the second switch is in its iirst or second position and to such heater only when the rst and second switches are in their rst position and the third switch is in its second position.

15. In combination, in a refrigeration system including a compressor, cooling coils, a defrosting heater adjacent saidcoils, a differential enclosure thermostat, a first control differential thermostat. a second control differential thermostat, and electrical connections interconnecting said three thermostats and said compressor and said heater whereby said heater is automatically cocked for subsequent energization by a predetermined low temperature adjacent the cooling coils and is energized upon the temperature adjacent the cooling coils rising to a. predetermined temperature.

16. In combination, in a refrigeration system including a compressor, cooling coils, a defrosting heater adjacent said coils, and an electrical actuating system including an enclosure thermostat, r

means for alternately energizing and deenergizing said compressor upon the occurrence of predetermined temperature in an enclosure being cooled, means for establishing a potential circuit through said heater upon the occurrence of a predetermined low temperature adjacent said cooling coils, means for energizing said heater upon the occurrence adjacent said cooling coils 10 of a higher predetermined temperature than the temperatures previously mentioned, and means for deenergizing said heater upon the occurrence adjacent said cooling coils of a. predetermined still higher temperature.

17. In combination, a refrigeration system including a compressor, a cooling coil, a housing therefor, a defroster heater adjacent the cooling coil, a differential cooled enclosure thermostat. a rst control differential thermostat, and a second control differential thermostat, said enclosure thermostat being set to snap olf at a predetermined low temperature of an enclosure being cooled and to snap on at a predetermined higher temperature, said rst and second control thermostats being electrically connected to each other and to the enclosure thermostat, to the heater, and to the compressor, the bulbs of the control thermostats being adjacent the cooling coil and in the housing therefor, said first and second control thermostats including two sets of contacts and a conductive arm movable therebetween and carrying the movable contacts Vof both sets, said first control thermostat being set to effect contact of one set of contacts at the predetermined maximum temperature adapted to snap the enclosure thermostat into on position and to effect contact of the other set of contacts at a predeterminedvhigher temperature, said second control thermostat being set to effect contact of one set of contacts at the predetermined minimum temperature of said enclosure thermostat and to effect contact of the other set of contacts at a higher temperature including the melting temperature of ice, the said one set of contacts of the second control thermostat being connected to the heater and the said other set of contacts thereof being connected to the compressor, the one set of contacts of said rst control thermostat being connected to said compressor and the said other set of contacts being connected to the conductive arm of said second control thermostat, said enclosure thermostat being connected to the said conductive arm of said first control thermostat.

JAMES B. BADER.

REFERENCES CITED The following references are of record in the le of this patent:

y UNITED STATES PATENTS Number 

